Piston for fuel injection pumps



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W. E. LElBlNG PISTON FOR FUEL INJECTION PUMPS Filed June 9, 1954 Il lllllll LI April 30, 1957 www f Iza 4 IN VEN TOR. l/I//uw E H5/NG'- PISTONFOR FUELINJECTION PUMPS William E. Leibing, Redwood City, Calif.

Application June 9, 1954, Serial No. 435,481

2 Claims.- (Cl. 309-12) My linvention relates to pistons for fuelinjection pumps and method of manufacture, and i-s a continuation-impartof my copending application Serial No. 348,067', filed April 10, 1953,Patent No. 2,725,861, issued December 6, 1955, for Injection Fuel Pumpfor Internal Combustion Engines. f

nited States Patent()l Fuel injection pumps are required to deliverextremely small quantities Vof fuel in extremely accurate amounts.

To accomplish this by means of a piston and cylinder, not only mustthere be an extremely close tit between the piston and cylinder, butalso the running clearances between a group of pistons and theircylinders must be extremely uniform. This has required the maintenanceof almost impossibly close manufacturing tolerances, for example, in therange of plus or minus tive hundred thousandths (.00005) for 'anominally one-half inch pis,- ton and cylinder.

It is a primary object `of my invention to provide a pump and method ofmanu-facture wherein the piston and cylinder may be manufactured withtolerances which can be readily maintained, and in the course ofassembly the dimensions of the piston may be altered to establish thenecessary close tolerance running tit with its mating piston; further,whereby a high degree of uniformity may be maintained without expensivemanufacturing procedures of the mating parts; and whereby in a multiplepiston pump the clearances m-ay be exactly mated even though thecylinder diameters should vary.

A further -o'bject of my invention is to provide a simple and effective-means and method of altering the piston diameter, which is applicablenot only in the initial manufacture of the fuel injection pump but alsoin effecting repair after the pump has worn.

With the above and other objects in view, as may appear hereinafter,reference is directed to the accompanying drawings, in which:

Figure 1 is a fragmentary partial sectional, partial elevational view ofa fuel injection pump, incorporating my piston;

Fig. 3 is a similar longitudinal, sectional view of a modified form of apiston with the surrounding vcylinder shown fragmentarily;

Fig. 4 is a partial sectional, partial elevational View of the partiallyprepared piston blank;

Fig. 5 is an elevational View of the expander member;

Fig. 6 is a partial sectional, partial elevational view, showing theexpander member in its preliminary inserted position; and

Fig. 7 is a similar view, showing the expander in its final position,before trimming the end of the expander and piston.

Reference is first directed to Fig. l, which illustrates a type of -fuelpump disclosed more completely in my latent 2,725,861. y

The fuel injection pump designated 1 includes a cylinder block 2 havinga' ring of parallel cylinders. Each cylinder is provided with a liner 3.Each cylinder receives a piston 4 having a cap 5, forming a socket to2,790,685 PatentedApr. 30, 1 957 fice receive the end of a connectingrod 6. The connecting rods are connected to suitably oscillatingmechanism, such as a wobble plate or other means, for elfectingreciprocation of the pistons.

One end of the cylinder block 2 is provided with a ydischarge manifold7, shown fragmentarily in Fig. l.

The discharge manifold is provided with a series of discharge valves 8,registering with corresponding cylinders.

Located within the cylinder block `2 and within the ring of cylinders isa il-oat chamber 9 in which is mounted a iloat 10, disclosed in moredetail in my Acopending application. The float controls inlet passages11 which radiate to the ring of cylinders. Each liner'la is providedwith an inlet slit 12 communicating with 'a corresponding inlet passage.

Another type of fuelinjection pump involves a plurality of cylinders 13having a counterbore 14 at one end. Each receives a pistonlS on which isiitted a collar 16 retained by a spring clip retaining ring 17. A returnspring 18 disposed between the collar 16 and 'base of the counte-rbore14 tends to maintain the piston 15 in a raised position relative to itscylinder 13. The end of the piston 15 is fitted with a bearing button 19adapted to be engaged by suitable means for depressing the piston.

The pistons 4 and 15 are essentially identical in that each one isprovided with a tapered bore 20 and a constricted Iaperture 21 at itshead end. In the case of the piston 4, the aperture 21 intersects asocket cooperating with the cap 5 to retain the end of the comiectingrod 6. ln the case of the pist-on 15, the aperture 21 receives `a stemfor retaining the bearing button 19. The tapered bores 20 of the pistons4 and 15 receive a tapered expander plug 22, the position of which inthe tapered bore 20 deter-mines the diameter of the piston.

In order for a fuel injection pump t-o operate sat-isfactorily, it isnecessary that each piston and its ycylinder deliver an accurate andrelatively minute amount of fluid. This necessitates an extremelyuniform fit between the pistons and their respective cylinders orliners, as the case may be. Heretofore, this has been accomplished byexpensive nishing operations in which it is necessary to hold thetolerances of the piston and cylinder to plus or minus five hundredthousandths (.00005). Not only is such accurate manufacturing expensive,by reason of the time and care required, lbuty at best the percentage ofrejection is extremely large. On the other hand, the manufacture of thecylinders or their liners to a tolerance plus or minus one-half athousandth (.0005) is well Within standard manufacturing techniques atonly a small fraction of the cost -for a higher order of tolerance.

My piston is primarily designed -so that its diameter may be variedminutely, in order that each piston may be individually fitted to acorresponding cylinder or liner without requiring excessively closetolerances iin the manufacture of the piston itself.

My method of manufacturing the piston is best illustrated with referenceto Figs. 4 through 7. The piston blank is machined from bar stock, itstapered bore 20 and aperture 21 drilled, and then externally threaded orgrooved, to form a rough blank of the pistons 4 or 15, as the case maybe. A tapered expander plug 22 is then formed and is initially somewhatlonger than the internally tapered skirt of the piston. It has beenfound satisfactory to employ a taper for the bore 20 and expander plug22 of one-fourth inch (1/4) per foot. However, a lesser taper ofone-eighth inch (l/s") per foot maybe used. The taper should be suchthat once in place the expander plug will not vibrate loose.

The expander plug 22 is inserted in its piston and forced thereinsuiiciently to expand the piston approximately one-thousandth totwo-thousandths of an inch (.001 to ,002). The piston is thencenter-less ground,

maintaining a tolerance of plus or minus one-half thoucorrespondingcylinder or liner and the clearance determined. One methodofaccomplishing this is by use of a conventional air measuring devicewhich measures the leakage of air past the piston. Such Va' device iscapable of indicating clearance in terms of a millionth of an inch.

After observing the clearance Yand noting' whether the piston is tooloose or too tight,` the expander p'lug is then forced axially a trialdistance and the' piston reinserted. This inherently is comparatively arapid' and dependable operation, resulting in a remarkably uniform fitbetween a series of pistons and their cylinders.` After the piston hasbeen tted, the excess end of itsskirt and the protriid# ing end of theexpander Vplugv are trimmed oi.

The piston expands uniformly, both axially` and circumferentially, andthe amount of needed expansion is well within the elastclimit of mostmaterials, for ex ample, stainless steel or aluminum bronze, so thatshould the fit be too tight, requiring retraction of the expansion plug,the piston contracts into'conformity therewith.

Having fully described my invention, it is to be understood that I donot wish to be limited to the details herein set forth but my inventionis of the full scope of the appended claims.

I claim:

1. A piston construction, comprising: a piston having an axiallyapertured head at one end and an internally tapered skirt extendingtherefrom, open at its extremity; and an expansion plug tting saidskirt, and accessible through said apertured head and the open end ofsaid skirt for axial movement, to expand and permit radial contractionof said skirt.

2 A piston construction as set forth in claim 1, wherein: the taper ofsaid skirt'and ysaid plug is such that said plug is frictionally held inits axially adjusted position within said skirt.

References Cited in the le of this patent UNlTED STATES PATENTS1,358,825 Busby Nov. 16, 1920 1,722,389 Opie et al. July 30, 19292,034,005 Six Mar. 17, 1936 2,405,938 Beeh Aug. 20, 1946 2,413,115Sheehan Dec. 24, 1946 FOREIGN PATENTS 729,480 France July 25, 1932

